MAORY + MICADO scientific analysis of the 1pfDM versus 2pfDM performance with realistic atmospheric profiles

Abstract

This document shows that the implementation of a 2nd pfDM in MAORY would have an impressive impact on the scientific productivity of MAORY+MICADO. An exhaustive analysis of the 1pfDM versus 2pfDM photometric, astrometric and sky coverage performances was carried out based on realistic atmospheric profiles that take into account a wide range of observing conditions. The effect of the 2nd pfDM is to increase image quality and its stability under variations of atmospheric turbulence and seeing conditions, and more dramatically for bluer filters than for redder ones. The 2nd pfDM also significantly improves the spatial homogeneity of the point spread function, allowing for the restoration of the full 2 arcmin MAORY field of view, with consequent impact on the natural reference stars region and on the sky coverage. In terms of scientific performances, this means: ●The sensitivity one can expect for a typical target in typical conditions will increase by 1 mag in K-band (equivalently 2 mag in H-band and over 3 mag in J-band). A 1 mag difference corresponds to a factor 6 reduction in telescope time to reach the same signal-to-noise on faint point sources. This is invaluable for deep integrations on faint targets as well as efficient use of telescope time. ● The fraction of targets for which a scientifically useful minimum Strehl ratio can be achieved (sky coverage) will increase by a factor 2-6 in K-band. This is invaluable for target selection as well as programme scheduling on the telescope. ● The astrometric accuracy over the (zoomed-in, reduced) MICADO FoV will be impacted by 20% in high SNR conditions (>200) corresponding to the range baseline-goal of the MAORY requirements. These results are of extreme importance because they are related to the selection of targets based primarily on astrophysical rather than on technical criteria as well as to the need to achieve good AO performance in moderate atmospheric conditions to enable efficient long integrations, as highlighted by Davies & Kasper (2012) among the lessons learned in their adaptive optics review. Indeed, without the 2nd pfDM there will be a significant loss for science cases about the dynamics of dense stellar systems and black holes in galaxies, while resolved stellar population, Galactic Centre, and galaxy evolution studies will be affected in a major way.